1. Field of the Invention
This invention relates to a semiconductor device and particularly relates to a semiconductor device having a horizontal-type nitride semiconductor element.
2. Background Art
Gallium nitride (GaN) has a larger band gap than that of silicon (Si), and therefore, a semiconductor element in which GaN is used has a higher critical electric field than that of a semiconductor element in which Si is used, and the element having a small size and a high breakdown voltage can be easily realized. Therefore, when a semiconductor element (power element) for controlling power is manufactured by using GaN, the element having low ON resistance and small loss can be realized. In particular, a HFET (heterostructure field-effect transistor) in which an AlGaN/GaN heterostructure is used has a simple element structure, and good characteristics can be expected (for example, JP-A 2003-229566 (Kokai)).
On the other hand, in the power supply circuit, a surge voltage is occasionally applied in power supply activation or the like. In this case, a breakdown voltage or more of voltage is occasionally applied to a power element in the power supply circuit. In a conventional power element in which Si is used, avalanche breakdown occurs by application of voltage of breakdown voltage or more to the p-n junction surface, and a current can be flowed while holding high voltage. Thereby, the power input by the surge is consumed in the power element to prevent the power element from breaking down, and parts except for the power element in the power circuit can also be prevented from breaking down.
However, in the above-described nitride semiconductor element in which GaN or the like is used, the p-type semiconductor layer has high contact resistivity, and therefore, even when avalanche breakdown occurs, a large avalanche current cannot be flowed. Therefore, even when the avalanche breakdown occurs, capacity of consuming the surge power is low, and high surge resistance cannot be obtained.